Porous polythiophene as a cathode material for lithium batteries with high capacity and good cycling stability

Polythiophene (PTh) has been synthesized by chemical oxidative polymerization and used as an active cathode material in lithium batteries. The lithium batteries are characterized by cyclic voltammetry (CV), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopic studies (EIS). The lithium battery with the PTh cathode exhibits a discharge voltage of 3.7 V compared to Li⁺/Li and excellent electrochemical performance. PTh can provide large discharge capacities above 50 mA h g⁻¹ and good cycle stability at a high current density 900 mA g⁻¹. After 500 cycles, the discharge capacity is maintained at 50.6 mA h g⁻¹. PTh is a promising candidate for high-voltage power sources with excellent electrochemical performance.     

Preparation and enhanced electrochemical properties of nano-sulfur/poly(pyrrole-co-aniline) cathode material for lithium/sulfur batteries

Poly(pyrrole-co-aniline) (PPyA) copolymer nanofibers were prepared by chemical oxidation method with cetyltrimethyl ammonium chloride (CTAC) as template, and the nano-sulfur/poly(pyrrole-co-aniline) (S/PPyA) composite material in lithium batteries was achieved via co-heating the mixture of PPyA and sublimed sulfur at 160 °C for 24 h. The component and structure of the materials were characterized by FTIR, Raman, XRD, and SEM. PPyA with nanofiber network structure was employed as a conductive matrix, adsorbing agent and firm reaction chamber for the sulfur cathode materials. The nano-dispersed composite exhibited a specific capacity up to 1285 mAh g⁻¹ in the initial cycle and remained 866 mAh g⁻¹ after 40 cycles.     

Application of gelatin as a binder for the sulfur cathode in lithium-sulfur batteries

Gelatin, a natural biological macromolecule, was successfully used as a new binder in place of poly(ethylene oxide) (PEO) in the fabrication of the sulfur cathode in lithium-sulfur batteries. The structure and electrochemical performance of the two types of sulfur cathodes, with gelatin and PEO as binders, respectively, were compared in 1 M LiClO₄ DME/DOL (V/V = 1/1) electrolyte. The results showed that the gelatin binder had multifunctional effects on the sulfur cathode: it not only functioned as a highly adhesive agent and an effective dispersion agent for the cathode materials, but also an electrochemically stable binder. The gelatin binder-sulfur cathode achieved a high initial capacity of 1132 mAh g⁻¹, and remained at a reversible capacity of 408 mAh g⁻¹ after 50 cycles, all of which were better than with the PEO binder-sulfur cathode under the same conditions.     

Polyterthiophene/CNT composite as a cathode material for lithium batteries employing an ionic liquid electrolyte

A polyterthiophene (PTTh)/multi-walled carbon nanotube (CNT) composite was synthesised by in situ chemical polymerisation and used as an active cathode material in lithium cells assembled with an ionic liquid (IL) or conventional liquid electrolyte, LiBF₄/EC-DMC-DEC. The IL electrolyte consisted of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄) containing LiBF₄ and a small amount of vinylene carbonate (VC). The lithium cells were characterised by cyclic voltammetry (CV) and galvanostatic charge/discharge cycling. The specific capacity of the cells with IL and conventional liquid electrolytes after the 1st cycle was 50 and 47 mAh g⁻¹ (based on PTTh weight), respectively at the C/5 rate. The capacity retention after the 100th cycle was 78% and 53%, respectively. The lithium cell assembled with a PTTh/CNT composite cathode and a non-flammable IL electrolyte exhibited a mean discharge voltage of 3.8 V vs Li⁺/Li and is a promising candidate for high-voltage power sources with enhanced safety.     

Synthesis and electrochemical performance of lithium vanadium oxide nanotubes as cathodes for rechargeable lithium-ion batteries

A new kind of cathode materials for rechargeable lithium-ion batteries, lithium vanadium oxide nanotubes synthesized by a combined sol-gel reaction and hydrothermal treatment procedure is reported in this paper. SEM, TEM, XRD and XPS techniques were performed to investigate the morphology and structure of the resulting materials. The results confirmed that the synthetic materials are composed of uniformly open-ended multiwalled nanotubes with a length from 1 to 3 μm. The inner and the outer diameters of the obtained nanotubes vary from 30 to 50 nm and 50 to 120 nm, respectively. The electrochemical performance as a cathode material was examined and evaluated by cyclic voltammetry, galvanostatic charge-discharge cycling and AC impedance spectroscopy techniques. The results indicated that the resultant lithium vanadium oxide nanotubes have a high initial discharge capacity of 457 mAh g⁻¹ in the potential range of 1.0-4.0 V (vs. Li/Li⁺) and good cycling performance. The improved electrochemical performance of the products should be due to its special one-dimensional multiwalled tubular structure and the contribution of lithium-ions.     

Electrochemical behavior of biphenyl as polymerizable additive for overcharge protection of lithium ion batteries

Electrochemical properties and working mechanism of biphenyl as a polymerizable electrolyte additive for overcharge protection of lithium ion batteries are studied by microelectrode voltammetry, charge-discharge measurements and SEM characterization of the overcharged cell’s components. The experimental results reveal that biphenyl can electrochemically polymerize at the overcharge potential of 4.5-4.75 V (versus Li/Li⁺) to form a layer of conductive film on the cathode surface and the polymer deposits may develop to penetrate the separator to reach the anode surface, resulting an internal short-circuit to prevent from the cell voltage runaway. On the other hand, the electro-oxidative polymerization of biphenyl produces excessive gas and heat, which help to enhance the sensitivities of electric disconnecting devices. In addition, it is also found that the use of biphenyl as an electrolyte additive does not significantly influence the normal performances of the lithium ion batteries.     

Preparation and performance of a core-shell carbon/sulfur material for lithium/sulfur battery

The core-shell carbon/sulfur material with high performance is prepared by a facile and fast deposit method in an aqueous solution. As sulfur ratio is 85% (w/w) in the composite, scanning electron microscope (SEM) and transmission electron microscope (TEM) observation show that the moniliform particles with 10 nm sulfur shells preserve the morphology of carbon cores. Tested as the cathode material in a lithium cell with binary organic electrolyte at room temperature, the composite shows excellent electrochemical performance. It exhibits a specific capacity up to 1232.5 mAh g⁻¹ at the initial discharge and its specific capacity remained above 800 mAh g⁻¹ after 50 cycles. Meanwhile, the composite also exhibits the high-rate behavior at 800 mA g⁻¹ of current density. Assuming a complete reaction to the final product, Li₂S, the utilization of the electrochemically active sulfur is about 85% at the initial cycle. Electrochemical impedance spectroscopy (EIS) is introduced to understand the impact of the microstructure of composite on electrochemistry. According to our study, a novel core-shell structural carbon/sulfur material is proposed and the key factors of the preparation are discussed.     

Electrochemical and ex situ XRD studies of a LiMn1.5Ni0.5O4 high-voltage cathode material

Sub-micro spinel-structured LiMn_1.5Ni_0.5O₄ material was prepared by a spray-drying method. The electrochemical properties of LiMn_1.5Ni_0.5O₄ were investigated using Li ion model cells, Li/LiPF₆ (EC + DMC)/LiMn_1.5Ni_0.5O₄. It was found that the first reversible capacity was about 132 mAh g⁻¹ in the voltage range of 3.60-4.95 V. Ex situ X-ray diffraction (XRD) analysis had been used to characterize the first charge/discharge process of the LiMn_1.5Ni_0.5O₄ electrode. The result suggested that the material configuration maintained invariability. At room temperature, on cycling in high-voltage range (4.50-4.95 V) and low-voltage range (3.60-4.50 V), the discharge capacity of the material was about 100 and 25 mAh g⁻¹, respectively, and the spinel LiMn_1.5Ni_0.5O₄ exhibited good cycle ability in both voltage ranges. However, at high temperature, the material showed different electrochemical characteristics. Excellent electrochemical performance and low material cost make this spinel compound an attractive cathode for advanced lithium ion batteries.     

Hydrothermal synthesis of carbon-coated lithium vanadium phosphate

A novel hydrothermal synthesis was developed to prepare carbon-coated lithium vanadium phosphate (Li₃V₂(PO₄)₃) powders to be used as cathode material for Li-ion batteries. The structural, morphological and electrochemical properties were investigated by means of X-ray powder diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and constant current charge-discharge cycling. This material exhibits high initial discharge capacity of 178, 173 and 172 mAh g⁻¹ at 0.1, 0.2 and 0.5 C between 3.0 and 4.8 V, respectively. Moreover, it displays good fast rate performance, which discharge capacities of 136, 132 and 127 mAh g⁻¹ can be delivered after 100 cycles between 3.0 and 4.8 V versus Li at a different rate of 1, 2 and 5 C, respectively. For comparison, the electrochemical properties of carbon-coated lithium vanadium phosphate prepared by traditional solid-state reaction (SSR) method are also studied.     

One step solid state synthesis of FeF3·0.33H2O/C nano-composite as cathode material for lithium-ion batteries

Nanometer-sized FeF₃·0.33H₂O/acetylene black composite has been synthesized by one step chemico-mechanical ball-milling process using Fe (NO₃)₃?9H₂O and NH₄F as precursors and investigated as cathode materials for secondary lithium batteries. The obtained FeF₃·0.33H₂O/C composite was described in terms of structure, morphology, and electro-chemical performance. The composite exhibited a noticeable capacity of 233.9 mAh g⁻¹ at a current density of 20 mA g⁻¹ within potential range 1.8–4.5 V and good rate capability. These results showed that FeF₃·0.33H₂O/C nano-composite prepared from an easily scalable chemico-mechanical ball-milling process was of great industrial interest.     

Comparison of 4 V and 3 V electrochemical properties of nanocrystalline LiMn2O4 cathode particles in lithium ion batteries prepared by ultrasonic spray pyrolysis

Nanocrystalline LiMn₂O₄ particles were prepared by an ultrasonic spray pyrolysis method using nitrate salts at 800 °C in air atmosphere. Particle properties were characterized by the X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy. In addition, cyclic voltammetry and galvanostatic tests were performed to investigate the effects of structure on electrochemical behavior of both the 4 V and 3 V potential plateaus. Particle characterization studies show that the nanocrystalline particles have spinel structure of submicron size with spherical morphology. Particles, ranging between 75 and 1250 nm, were formed by aggregation of nanoparticles. Discharge capacity of LiMn₂O₄ particles between 3.0 and 4.5 V is 70 mA h g⁻¹ and cumulative capacity between 2.2 and 4.5 V is 111 mA h g⁻¹ at 0.5 C rate. Discharge capacity at the 4 V potential region reduces to 47% of initial capacity, whereas cumulative capacity fade is 62% after 100 cycles at 0.5 C rate. Although nanocrystalline LiMn₂O₄ cathode particles exhibit good rate capability at the 4 V plateau, capacity decreased rapidly by increasing C- rates and cycling between 2.2 and 4.5 V. The loss of capacity can be attributed to phase transformation and dissolution of electrode material. Particle characterization of used cathodes showed that nanocrystalline LiMn₂O₄ electrodes partly dissolve during electrochemical cycling.     

The preparation of nano-sulfur/MWCNTs and its electrochemical performance

In this work, a novel nano-sulfur/MWCNTs composite with modified multi-wall carbon nano-tubes (MWCNTs) as sulfur-fixed matrix for Li/S battery is reported. Based on different solubility of sulfur in different solvents, nano-sulfur/MWCNTs composite was prepared by solvents exchange method. The composite was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The modified MWCNTs are considered that not only acts as a conducting material, but also a matrix for sulfur. The electrochemical performance of the nano-sulfur/MWCNTs composite was tested. The results indicated that nano-sulfur/MWCNTs composite had the specific capacity of 1380 mAh g⁻¹, 1326 mAh g⁻¹ and 1210 mAh g⁻¹ in the initial cycle at 100 mA g⁻¹, 200 mA g⁻¹ and 300 mAh g⁻¹ discharge rates respectively, and remained a reversible capacity of 1020 mAh g⁻¹, 870 mAh g⁻¹ and 810 mAh g⁻¹ after 30 cycles. The electrochemical performances confirm that the modified MWCNTs as sulfur-fixed matrix show better ability than any other carbon in cathode of Li/S batteries that had been reported.     

Nano/micro-hybrid NiS cathodes for lithium ion batteries

The present study highlights a low temperature process by which 1D stacked 3D microstructures of nickel sulfide comprised of nanospikes have been synthesized and assembled as cathodes for lithium chalcogenide batteries. These micro/nano-clusters were synthesized hydrothermally under different conditions. These clusters exhibited a surface area of 15 m² g⁻¹. The present study also provides the first reports on the electrochemical performance of these NiS microclusters as cathode materials in lithium fluoro-Tris-sulfonimide electrolyte for lithium ion batteries. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic behavior and specific capacity. This electrode−electrolyte combination showed minimal dissolution of the electrode in the electrolyte which was confirmed by inductively coupled plasma atomic emission spectroscopy. From the electrochemical analysis performed an intrinsic correlation between the capacity, self-discharge property and the surface morphology has been deduced and explained on the basis of relative contributions from the redox reactions of nickel sulfide in lithium fluoro-Tris-sulfonimide electrolyte. A working model of lithium battery in a coin cell form is also shown exhibiting a specific capacity of 550 mAh g⁻¹.     

Preparation of poly(acrylonitrile-butyl acrylate) gel electrolyte for lithium-ion batteries

Poly(acrylonitrile-butyl acrylate) gel polymer electrolyte was prepared for lithium ion batteries. The preparation started with synthesis of poly(acrylonitrile-butyl acrylate) by radical emulsion polymerization, followed by phase inversion to produce microporous membrane. Then, the microporous gel polymer electrolytes (MGPEs) was prepared with the microporous membrane and LiPF₆ in ethylene carbonate/diethyl carbonate. The dry microporous membrane showed a fracture strength as high as 18.98 MPa. As-prepared gel polymer electrolytes presented ionic conductivity in excess of 3.0 × 10⁻³ S cm⁻¹ at ambient temperature and a decomposition voltage over 6.6 V. The results showed that the as-prepared gel polymer electrolytes were promising materials for Li-ion batteries.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

Enhanced lithium storage in a VO2(B)-multiwall carbon nanotube microsheet composite prepared via an in situ hydrothermal process

A novel VO₂(B)-multiwall carbon nanotube (MWCNT) composite with a sheet-like morphology was synthesized by a simple in situ hydrothermal process. The morphology and structural properties of the samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). FE-SEM observations demonstrated that the nanosheets are frequently grown together in the form of bundles composed of numerous nanosheets, each with a smooth surface and a typical length of 300-500 nm, width of 50-150 nm, and thickness of 10-50 nm. Electrochemical measurements were carried out using different discharge cut-off voltages. Electrochemical tests show that the VO₂(B)-MWCNT composite cathode features long-term cycling stability and high discharge capacity (177 mAh g⁻¹) in the voltage range of 2.0-3.25 V at 1 C with a capacity retention of 92% after 100 cycles. The electrochemical impedance spectra (EIS) indicate that the VO₂(B)-MWCNT composite electrode has very low charge-transfer resistance compared with pure VO₂(B), indicating the enhanced ionic conductivity of the VO₂(B)-MWCNT composite. The enhanced cycling stability is attributed to the fact that the VO₂(B)-MWCNT composite can prevent the aggregation of active materials, accommodate the large volume variation, and maintain good electronic contact. We strongly believe that the VO₂(B)-MWCNT composite can be considered as a potential cathode material for lithium-ion batteries.     

Differential scanning calorimetry analysis of an enhanced LiNi0.8Co0.2O2 cathode with single wall carbon nanotube conductive additives

The replacement of traditional conductive carbon additives with single wall carbon nanotubes (SWCNTs) in lithium metal oxide cathode composites has been shown to enhance thermal stability as well as power capability and electrode energy density. The dispersion of 1 wt% high purity laser-produced SWCNTs in a LiNi_0.8Co_0.2O₂ electrode created an improved percolation network over an equivalent composite electrode using 4 wt% Super C65 carbon black; evidenced by additive connectivity in SEM images and an order of magnitude increase in electrode electrical conductivity. The cathode with 1 wt% SWCNT additives showed comparable active material capacity (185–188 mAh g⁻¹), at a low rate, and Coulombic efficiency to the cathode composite with 4 wt% Super C65. At increased cycling rates, the cathode with SWCNT additives had higher capacity retention with more than three times the capacity at 10C (16.4 mA cm⁻²). The thermal stability of the electrodes was evaluated by differential scanning calorimetry after charging to 4.3 V and float charging for 12 h. A 40% reduction of the cathode exothermic energy released was measured when using 1 wt% SWCNTs as the additive. Thus, the results demonstrate that replacing traditional conductive carbon additives with a lower weight loading of SWCNTs is a simple way to improve the thermal transport, safety, power, and energy characteristics of cathode composites for lithium ion batteries.     

Novel tin-graphite composites as negative electrodes of Li-ion batteries

For the purpose of obtaining an improved performance of the graphite negative electrode of Li-ion batteries, a novel graphite-tin composite has been synthesized by reduction of tin chloride (SnCl₂) with KC₈ in THF medium. This composite contains nano-sized tin particles dispersed on the graphite surface and free tin aggregates. Lithium electrochemical insertion occurs both in graphite and in tin. An experimental reversible specific charge of 489 mA h g⁻¹ is found stable upon cycling. Such a value is lower than the maximum theoretical one of 609 mA h g⁻¹ suggesting that only a part of tin is involved in the lithium insertion/extraction process. This part of active tin responsible for the stable capacity could be that bound to graphite. To the contrary, free tin aggregates could contribute to an extra capacity that decreases upon cycling in relation with the volume changes that occurs during alloying/dealloying.     

Electrochemical reaction of the SiMn/C composite for anode in lithium ion batteries

The SiMn-graphite composite powder was prepared by mechanical ball milling and its electrochemical performances were evaluated as the candidate anode materials for lithium ion batteries. It is found that the cyclic performance of the composite materials is improved significantly compared to SiMn alloy and pure silicon. The heat treatment of the electrodes is beneficial for enhancing the cyclic stabilities. The SiMn-20 wt.% graphite composite electrode after annealing at 200 °C has an initial reversible capacity of 463 mAh g⁻¹ and a charge-discharge efficiency of 70%. Moreover, the reversible capacity maintains 426 mAh g⁻¹ after 30 cycles with a coulomb efficiency of over 97%. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electron microscopy. The lithiation/delithiation behavior was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composite materials appear to be promising candidates as negative electrodes for lithium rechargeable batteries.     

Layered lithium transition metal nitrides as novel anodes for lithium secondary batteries

We report the approach to overcome the deterrents of the hexagonal Li_2.6Co_0.4N as potential insertion anode for lithium ion batteries: the rapid capacity fading upon long cycles and the fully Li-rich state before cycling. Research reveals that the appropriate amount of Co substituted by Cu can greatly improve the cycling performance of Li_2.6Co_0.4N. It is attributed to the enhanced electrochemical stability and interfacial comparability. However, doped Cu leads to a slightly decreased capacity. High energy mechanical milling (HEMM) was found to effectively improve the reversible capacity associated with the electrochemical kinetics by modifying the active hosts’ morphology characteristics. Moreover, the composite based on mesocarbon microbead (MCMB) and Li_2.6Co_0.4N was developed under HEMM. The composite demonstrates a high first cycle efficiency at 100% and a large reversible capacity of ca. 450 mAh g⁻¹, as well as a stable cycling performance. This work may contribute to a development of the lithium transition metal nitrides as novel anodes for lithium ion batteries.